A study is being made of the redox and alkylation reactions of vitamin B12 compounds. The electroanalytical method of pulse polarography and various spectroscopic methods are being used to measure the concentrations of B12 compounds in order to determine stoichiometry and reaction kinetics. Specific reactions being studied are those of vitamin B12a and B12r with thiols and sulfides. The vitamin B12r is prepared using controlled potential reduction of a Pt electrode. In addition the reactions of alkyl halides with Vitamin B12r which has been complexed by thiols is to be studied in order to determine stoichiometry and kinetics. Other aspects of this project involve determining reduction potentials and rates and mechanisms of heterogeneous electron transfer processes for various corrinoid couples.